1. Field of the Invention
The invention relates to a surveying apparatus comprising a device for determining the height above a point on the ground, according to the preamble of patent claim 1.
2. Description of the Related Art
For geodetic surveying, it is necessary to know sufficiently accurately the height of the surveying apparatus above a reference point on the ground. In the case of a surveying apparatus described in DE 198 02 379 A1, an infrared distance measuring device also suitable for horizontal distance measurements is used for measuring the height of the apparatus above the ground. For this purpose, the telescope is equipped with a front attachment which deflects the emitted light beam around the index arm and the head of the stand carrying the surveying apparatus and directs said light beam at the point on the ground. The front attachment contains a plane mirror with adjustable inclination. A measuring processor determines the height of the horizontal axis of the telescope above the point on the ground from the measured length of the distance from the horizontal axis via the plane mirror to the point on the ground and the angle which the plane mirror makes with the optical axis of telescope. In another version of the surveying apparatus, the height of the horizontal axis above the point on the ground is determined from the angle which the optical axis of the telescope makes with the horizontal and the angle which the plane mirror makes with the optical axis of the telescope.
The determination of the angle between plane mirror and optical axis of the telescope is relatively inaccurate. However, small errors in measurement have a considerable effect on the accuracy of the calculated height. The use of the apparatus for precise surveying tasks is therefore problematic. Moreover, the angle measurement at the plane mirror is carried out manually. The angle value must therefore be communicated to the measuring processor by input on a keyboard.
It is the object of the invention to improve a measuring apparatus of the type stated at the outset in such a way that the height determination can be effected more accurately.
According to the invention, this object is achieved by a surveying apparatus according to the features of patent claim 1.
Instead of a plane mirror, as in the surveying apparatus according to the prior art, a reflector which simultaneously effects beam divergence is used for beam deflection in a surveying apparatus according to the invention. The divergence angle of the divergence beam is adjusted so that the point on the ground is always illuminated for the heights possible during operation. A reflector arranged at the point on the ground enables the distance measuring device in the apparatus to measure the distance of the point on the ground from the axis of rotation or horizontal axis of the telescope via the beam deflection.
Expediently, the position of the telescope can be variable and is determined for the height determination. The angle of tilt of the telescope is available through an angle-of-tilt encoder which is in any case present. A processor-assisted evaluation device uses trigonometric relationships to calculate therefrom the height of the horizontal axis of the telescope above the reflector arranged at the point on the ground.
Distance and angle measurement are performed with the usual high accuracy of measurement of the apparatus, so that the height above the point on the ground can be sufficiently accurately determined. Since distance and angle measurement have been carried out to date under processor control, the height measurement can be automated by simple software modification.
For beam deflection and simultaneous beam divergence, a convex mirror or a prism having a curved reflecting surface or an appropriate combination of mirror, lens and/or prism is suitable. Preferably, the infrared or laser beam emitted by the telescope is caused to diverge in a vertical plane, i.e. the plane perpendicular to the horizontal axis. The mirror or the mirror/lens/prism combination causes the emitted light beam to diverge to such an extent that, with an approximately horizontal position of the telescope, the light striking the ground illuminates the point on the ground at the customary working heights, for example between 1.00 m and 2.20 m. Exact sighting of the point on the ground is not necessary. With a beam divergence in the horizontal direction too, the points on the ground which are slightly outside the plumb line under the apparatus can also be used for the height measurement.
Particularly in the case of motor-powered apparatuses, the control of the apparatus can be programmed so that the height measurement takes place fully automatically. Manual height input is no longer necessary.
The invention is explained in detail below with reference to the embodiment shown in the drawing. Corresponding elements are provided with the same reference symbols.